Re: The Very Terrible Twos.
how consistant are you with decipline, he needs to be punished each and every time without exception with he does one of the offending behaviours. Also, how long are you giving the punishments to work, it may take a few weeks for it to kick in. for the next month, consistantly put him in time out when he missbehaves, if your at the park or a friends house leave immediatly, no chances, ask once, if he doesn't stop then leave, if your at the grocery store or park leave, it sounds like a pain for you, but it will work. No treats etc if he acts up, give him nothing but his regular meals and snacks, no extra's. Take away something he values. At 2 1/2 it's hard to say what he will understand, but time outs and having to leave the park or a friends house he will understand. Explain to him why it's wrong to hurt people (2 year olds don't understand that their actions hurts someone else, they are still very self centered). If he gets away with it even once he will always do it, getting away with it just reinforces the bad behaviour. In the begining it will probably seem as if he's always in time out and you may feel guilty, but don't, it's for the best and once he catches on that it's not ok to hurt others (or whatever other bad behaviour he is doing) he will start to improve.
A few things to watch out for is that if you try to fix all of his problems at once it will be too much, make a list of what behaviours you would like him to stop and work on 1 or 2 of them at a time (ie, start with the worst ones first, hurting others), that doesn't mean you let anything slide, it just means you use other tactics, distration, removal from the situation etc rather than time out. The time out spot should be a quiet spot (careful if you are using his room, some kids will start to associate their rooms with being punished and not want to go to bed etc) with little or no distraction, there should be no discussion about time out, tell him what he did wrong and that he's having a time out, thats it, no other conversation, sit him ina chair in the corner and leave him there for a min or two (too long and he'll forget why he's there) and then say something like are you ready to be nice etc....if he's still angry he's not ready to get out, wait another 30seconds or so and try again.
Some things to keep an eye on are sleep, i know with my kids if they didn't sleep well the night before they are unmanagable the next day, (esp at 2) so he may need a nap rather than a time out, also, my kids got very irratable if they didn't eat much and are hungry, my son used to be like night and day at that age if he missed a snack or didn't eat much at a meal time.
The key is consistancy with when and what he is punished for, the actual punishment and all parents and caregivers need to be on the same page.
If you have done all of this and it hasn't worked than i would suggest taking him to see a doctor just to make sure there isn't something else going on with him.